Experiments and modelling of combined PVD and CVD processes using a hollow cathode arc discharge plasma

Abstract

Abstract A plasma-based deposition method was developed which allows the formation of non-metallic coatings with a graded metal interlayer to improve the substrate adhesion of the non-metallic coating. For this a plasma-enhanced PVD process was combined with a CVD process using a hollow cathode arc discharge plasma produced from a LaB 6 cathode as thermal electron emitter. In the present experiments layers which consist of a combination of an Al interlayer with a graded transition to an a-C:H top coating were deposited. The metal atoms needed for the interlayer formation were introduced into the plasma by evaporation, ionised by the plasma and deposited on the substrate. Subsequently, by introducing hydrocarbon precursor gases into the same discharge, the a-C:H coating was deposited. During the deposition the energy of the ions can be controlled by applying a negative r.f. bias potential to the substrate. The a-C:H top coating had a thickness of up to 3 μm. The thickness of the Al and the mixed Al–C interface was 0.3–0.8 μm. Parallel to the experimental work a space-resolved numerical model was developed to analyze the plasma processes which lead to the deposition of the coating. The results of the calculations were density profiles of the relevant gas phase species and deposition rates which can be compared with experimental values.